2. 1 nanometer (nm) = one billionth of a meter
What is a Virus?
1 nanometer (nm) = one billionth of a meter
100 nm
eukaryotics cells 10, ,000 nm
viroids nm
viruses nm
prokaryotics cells ,000 nm
prion 2-10 nm
Virus: A biological particle composed of nucleic acid and protein
Intracellular Parasites: organism that must “live” inside a host

3. All Have:
1) Capsid: coat of protein that surrounds nucleic acid
2) Nucleic Acid: RNA or DNA
Some Have:
Tail Fibers: Used for attachment (not legs)
Shape & size varies
Virus
Parts

4. Viral Replication
Bacteriophages (viruses that attack bacteria) are often studied
Replication is similar with many animal viruses
Two “life” cycles: Lytic & Lysogenic
Dozens of phage viruses attacking an E. coli bacteria cell
The bacteria cell is destroyed and new viruses escape

5. The Lytic Cycle 1st Step: Attachment Virus lands on cell membrane
Virus attaches to a cell receptor
Virus acts as key; receptor acts as lock
No attachment = No infection

6. The Lytic Cycle 2nd Step: Entry Virus enzyme weakens cell membrane
endocytosis
2nd Step: Entry
Virus enzyme weakens cell membrane
Genetic material (DNA or RNA) enters host cell

7. The Lytic Cycle 3rd Step: Replication
Virus DNA/RNA uses ribosomes to make virus proteins
Virus proteins created by transcription/ translation
transcription
translation
Viral DNA
Viral RNA
Viral Proteins

8. The Lytic Cycle 4th Step: Assembly
New virus proteins are assembled in the cytoplasm

9. The Lytic Cycle 5th Step: Release
Virus enzyme causes cell membrane to lyse (burst)
Viruses are released to find new host
Cycle repeats

10. All stages on one slide Attachment Entry Replication & Assembly
Release

12. The Lysogenic Cycle 1st step: Attachment = Same as lytic cycle
2nd Step: Entry = Same as lytic cycle

13. The Lysogenic Cycle 3rd step: Replication Provirus Created
Virus DNA combines with cell DNA
Infected cell divides by mitosis and copies the provirus
Each new cell will contain the provirus
Virus DNA
Pro-virus
cell DNA
Pro-virus
Pro-virus

14. The Lysogenic Cycle 5th Step: Release 4th Step: Assembly:
Same, except many cells burst releasing many more viruses
4th Step: Assembly:
After long period of dormancy, viral DNA is triggered and many new viruses are assembled in many cells

15. The viral DNA become active and starts making new viral proteins
The infected cells burst…releasing the new viruses

17. The Lysogenic Cycle The Lytic Cycle This happens VERY QUICKLY Examples
Virus attaches to host cell
Host cell assembles virus
Virus is released to infect other cells
This happens VERY QUICKLY
Usually makes person sick within hours
Examples
Flu/common cold
Chicken pox
HIV
Virus attaches to host cell
Viral DNA is dormant (hidden) inside host cell DNA
Host cell replicates with viral DNA inside
Viral DNA is then triggered by environmental factors and begins assembly and release
This takes a LONG PERIOD OF TIME
May take years before person gets sick from this virus
Examples
Shingles (dormant when a person gets the chicken pox)
AIDS (dormant when a person gets HIV)

18. HIV/AIDS

19. ReView
True or False: All viruses have a capsid, nucleic acid, and tail fibers.
List 3 reasons why viruses may be living? Nonliving?
What is the virus capsid made from?
What type of organism do phages infect?
In order list the stages of the lytic/lysogenic cycles.
In which stage…
does the host cell explode?
are virus proteins built to make new viruses?
is a provirus created?
does a virus connect with the host cell’s receptors?
Which two objects make up a provirus?
Which virus “life” cycle is considered the most harmful? Why?